The production of polymers utilizing renewable resources has been a field of increasing interest for many years. One particular area of interest concerns the production of polymers, specifically polyesters, which may be formed from polymerization of lactic acid-based monomers. Specifically, ring-opening polymerization of lactide has shown promise in production of polymeric materials. Lactic acid-based materials are often of particular interest as the raw materials can be derived from renewable resources (e.g., corn, plant starches, and canes).
Various approaches have been attempted to obtain lactide-based polymeric materials having desired product characteristics. For example, copolymerization with other materials and preparation of substituted polylactides have been examined extensively. For instance, Chen, et al. (‘Synthesis and Characterization of [L]-Lactide-Ethylene Oxide Multiblock Copolymers’, Macromolecules, 1997, 30(15), 4295–4301) have examined direct copolymerization of lactide with oxirane using a wide range of tin and aluminum based organometallic catalysts.
The polymers obtained by such methods tend to have very limited applications, though some polylactide products based upon lactide alone are beginning to show possible association in some fiber and film technologies. Limitation to wider product applicability has been primarily due to the low glass transition temperatures of the polylactide products. In general, products obtained to date have a glass transition temperature (Tg) of about 60° C. or less.
Another problem encountered with lactic acid-based polymeric materials has been a lack of hydrolytic stability. For example, the hydrolytic stability of the polymers is often such that they degrade too quickly during use, rendering them unsuitable for many applications.
What is needed in the art are polymeric materials capable of displaying improved hydrolytic and thermal performance which may be produced from raw materials including those derived from renewable resources.